Special Issue "Inorganic Layered Crystals: From Fundamentals to Materials Performance"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystalline Materials".

Deadline for manuscript submissions: closed (30 June 2019).

Special Issue Editors

Dr. Wei Cao
E-Mail Website
Guest Editor
Nano and Molecular Systems Research Unit, Faculty of Science, University of Oulu, BOX 3000 FIN-90014, Finland
Interests: materials physics; inorganic layered crystals; first-principles calculation; synchrotron techniques; synthetic crystals
Prof. Sergio E. Ulloa
E-Mail Website
Guest Editor
Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA
Interests: structure and electronic properties of materials; low-dimensional systems and electronic correlations
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

The exploration of inorganic layered crystals (ILCs), following the carbon analogues of graphite and graphene, has been greatly expanded in the past decade since pioneer findings of the exceptional semiconducting and optical properties of ILCs in their monolayer form. Multifunctional materials in their own rights, ILCs are rich in composition and behaviour, leading to wide potential applications in various domains covering magnetism, catalysis, electronics, and optics. Besides naturally occurring species, synthetic layered composites and heterojunctions further enrich the ILC families and meet specific materials properties beyond two dimensions (2D).

Based on emerging studies and promising functionalities of ILCs, this Special Issue is dedicated to providing a platform to the discussion, investigation, and review of recent progress of ILCs in 2D and 3D forms. The design, characterization and functionalization will be addressed, along with fundamental knowledge to reveal physical mechanisms beyond materials performance.

Topics within the Special Issue specifically emphasize (but are not limited to):

  • Synthetic protocols, from conceptual design to structural optimization, and experimental realization
  • Theoretical progress and predictions of novel functionalities and novel inorganic layered crystals
  • Materials synthesis and engineering routes for inorganic layered crystals and their heterojunctions
  • Decorating inorganic layered crystals for tailored functionalities
  • Cross-dimensional activation of inorganic layered crystals
  • Novel characterizations for structural and functional determination
  • Physical mechanisms beyond materials functionalities
  • Proximity-induced novel behaviour of composite inorganic layered crystals

There has been an explosive growth in synthesis, characterization and diverse device designs using inorganic layered crystal materials.  This Special Issue provides a forum to discuss and propose new developments and review recent successes in this most fertile field.

Dr. Wei Cao
Prof. Sergio E. Ulloa
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • van der Waals materials
  • Inorganic layered crystals
  • Materials functionalities
  • Materials design
  • Advanced characterizations
  • Computational materials sciences

Published Papers (6 papers)

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Research

Open AccessArticle
All-Inorganic Red-Light Emitting Diodes Based on Silicon Quantum Dots
Crystals 2019, 9(8), 385; https://doi.org/10.3390/cryst9080385 - 26 Jul 2019
Abstract
We report herein an all-inorganic quantum dot light emitting diode (QLED) where an optically active layer of crystalline silicon (Si) is mounted. The prototype Si-QLED has an inverted device architecture of ITO/ZnO/QD/WO3/Al multilayer, which was prepared by a facile solution process. [...] Read more.
We report herein an all-inorganic quantum dot light emitting diode (QLED) where an optically active layer of crystalline silicon (Si) is mounted. The prototype Si-QLED has an inverted device architecture of ITO/ZnO/QD/WO3/Al multilayer, which was prepared by a facile solution process. The QLED shows a red electroluminescence, an external quantum efficiency (EQE) of 0.25%, and luminance of 1400 cd/m2. The device performance stability has been investigated when the device faces different humidity conditions without any encapsulation. The advantage of using all inorganic layers is reflected in stable EQE even after prolonged exposure to harsh conditions. Full article
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Open AccessCommunication
Zeolite-Assisted Shear Exfoliation of Graphite into Few-Layer Graphene
Crystals 2019, 9(8), 377; https://doi.org/10.3390/cryst9080377 - 24 Jul 2019
Abstract
A novel method is presented to prepare few-layer graphene (FLG) in N-methyl-2-pyrrolidinone (NMP) by using a simple, low-cost and energy-effective shear exfoliation assisted by zeolite and using a cappuccino mixer to produce shear. We propose that the exfoliation of natural graphite flakes can [...] Read more.
A novel method is presented to prepare few-layer graphene (FLG) in N-methyl-2-pyrrolidinone (NMP) by using a simple, low-cost and energy-effective shear exfoliation assisted by zeolite and using a cappuccino mixer to produce shear. We propose that the exfoliation of natural graphite flakes can be achieved using inelastic collisions between graphite flakes and zeolite particles in a dynamic colloidal fluid. To confirm the exfoliation of FLG, spectroscopy and morphological studies are carried out using Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Additionally, the obtained graphene shows a linear flow of current and low resistance. The proposed method shows great promise for the industrial-scale synthesis of high-quality graphene with potential applications in future graphene-based devices, and furthermore, this method can be extended to exfoliate inorganic layered materials such as BN and MoS2. Full article
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Open AccessArticle
Growth of Multi-Layer hBN on Ni(111) Substrates via MOCVD
Crystals 2019, 9(7), 339; https://doi.org/10.3390/cryst9070339 - 02 Jul 2019
Abstract
In this paper we demonstrate a metal organic chemical vapor deposition (MOCVD) process for growth of few layer hBN films on Ni(111) on sapphire substrates using triethylborane (TEB) and ammonia (NH3). Ni(111) was selected as a substrate due to its symmetry [...] Read more.
In this paper we demonstrate a metal organic chemical vapor deposition (MOCVD) process for growth of few layer hBN films on Ni(111) on sapphire substrates using triethylborane (TEB) and ammonia (NH3). Ni(111) was selected as a substrate due to its symmetry and close lattice matching to hBN. Using atomic force microscopy (AFM) we find hBN is well aligned to the Ni below with in plane alignment between the hBN zig zag edge and the <110> of Ni. We further investigate the growth process exploring interaction between precursors and the Ni(111) substrate. Under TEB pre-exposure Ni-B and graphitic compounds form which disrupts the formation of layered phase pure hBN; while NH3 pre-exposure results in high quality films. Tunnel transport of films was investigated by conductive-probe AFM demonstrating films to be highly resistive. These findings improve our understanding of the chemistry and mechanisms involved in hBN growth on metal surfaces by MOCVD. Full article
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Open AccessArticle
High-Responsivity Photovoltaic Photodetectors Based on MoTe2/MoSe2 van der Waals Heterojunctions
Crystals 2019, 9(6), 315; https://doi.org/10.3390/cryst9060315 - 19 Jun 2019
Abstract
Van der Waals heterojunctions based on transition metal dichalcogenides (TMDs) show promising potential in optoelectronic devices, due to the ultrafast separation of photoexcited carriers and efficient generation of the photocurrent. Herein, this study demonstrated a high-responsivity photovoltaic photodetector based on a MoTe2 [...] Read more.
Van der Waals heterojunctions based on transition metal dichalcogenides (TMDs) show promising potential in optoelectronic devices, due to the ultrafast separation of photoexcited carriers and efficient generation of the photocurrent. Herein, this study demonstrated a high-responsivity photovoltaic photodetector based on a MoTe2/MoSe2 type-II heterojunction. Due to the interlayer built-in potential, the MoTe2/MoSe2 heterojunction shows obvious photovoltaic behavior and its photoresponse can be tuned by the gate voltage due to the ultrathin thickness of the heterojunction. This self-powered photovoltaic photodetector exhibits an excellent responsivity of 1.5 A W−1, larger than previously reported TMDs-based photovoltaic photodetectors. Due to the high-efficiency separation of electron-hole pairs and ultrafast charge transfer, the light-induced on/off ratio of current switching is larger than 104 at zero bias, and the dark current is extremely low (~10−13 A). These MoTe2/MoSe2 type-II heterojunctions are expected to provide more opportunities for future nanoscale optoelectronic devices. Full article
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Open AccessArticle
Ion Transport Behavior through Thermally Reduced Graphene Oxide Membrane for Precise Ion Separation
Crystals 2019, 9(4), 214; https://doi.org/10.3390/cryst9040214 - 20 Apr 2019
Abstract
The cation transport behavior of thermally treated reduced graphene oxide membranes (GOMs) is reported. The GOMs were reduced by heat treatment at 25, 80, and 120 °C and then characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy to [...] Read more.
The cation transport behavior of thermally treated reduced graphene oxide membranes (GOMs) is reported. The GOMs were reduced by heat treatment at 25, 80, and 120 °C and then characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy to determine oxygen group content, C/O ratio, and layer spacing. The permeation rates of various cations with different sizes and charge numbers through these membranes were measured to understand the effect of the cations on transport behavior. The results indicated that the cation transport through the membranes depended on the layer spacing of the membrane and ion size and charge. Cations of the same valence permeating through the same GOM could be differentiated by their hydration radius, whereas the same type of cation passing through different GOMs could be determined by the spacing of the GOM layers. The cation valence strongly affected permeation behavior. The GOM that was prepared at 120 °C exhibited a narrow layer spacing and high separation factors for Mg/Ca, Mg/Sr, K/Ca, and K/Fe. The cations moving through the membrane could insert into the membrane lamellas, which neutralized the negative charge of the membrane, enlarged the layer spacing of the GOMs, and affected cation permeation. Full article
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Open AccessArticle
Structural and Magnetoresistance Properties of Transfer-Free Amorphous Carbon Thin Films
Crystals 2019, 9(3), 124; https://doi.org/10.3390/cryst9030124 - 28 Feb 2019
Abstract
The control of the morphologies and thus the optical, electrical, and magnetic effect of 2D thin films is a challenging task for the development of cost-efficient devices. In particular, the angular dependent magnetoresistance (MR) of surface thin films up to room temperature is [...] Read more.
The control of the morphologies and thus the optical, electrical, and magnetic effect of 2D thin films is a challenging task for the development of cost-efficient devices. In particular, the angular dependent magnetoresistance (MR) of surface thin films up to room temperature is an interesting phenomenon in materials science. Here, we report amorphous carbon thin films fabricated through chemical vapor deposition at a SiO2 substrate. Their structural and angular magnetoresistance properties were investigated by several analytical tools. Specifically, we used a physical property measurement system to estimate the magnitude of the angular MR of these as-prepared sample thin films from 2 K to 300 K. An angular MR magnitude of 1.6% for the undoped a-carbon thin films was found up to 300 K. Under the magnetic field of 7 T, these films possessed an angular MR of 15% at a low temperature of 2 K. A high disorder degree leads to a large magnitude of MR. The grain boundary scattering model was used to interpret the mechanism of this angular MR. Full article
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